1. Field of the Invention
The present invention relates to an internal combustion engine with a cam phase change mechanism capable of changing the phase of an intake cam.
2. Description of the Related Art
Conventionally, there are internal combustion engines that comprise a cam phase change mechanism as a variable valve gear, which changes the phase of an intake cam to vary the opening and closing timings of an intake valve. Further, a technique has been developed in which the cam phase change mechanism is applied to internal combustion engines that are provided with a plurality of intake valves for each cylinder. According to this technique, the opening and closing timings of only some of the intake valves are varied in accordance with the engine load and speed.
In one such internal combustion engine, the opening and closing timings of some of the intake valves are delayed in, for example, a high-load, high-speed mode, whereby the open period of the intake valves, including those which are not subjected to delay-angle control, is extended to increase the flow rate of intake air for the security of output (Jpn. Pat. Appln. KOKAI Publication No. 3-202602).
In the internal combustion engine described in the above patent document, however, the closing timing of each intake valve is set so as not to be greatly delayed relative to the bottom dead center, whereby blowback is prevented, in order to ensure stable combustion in a low-speed mode. Thus, a long valve-open period cannot be secured, and the fuel efficiency may be reduced by pumping loss.